The present invention relates to decanter systems and in particular, to decanter systems for utilization with wastewater treatment reactors.
Certain wastewater treatment processes, especially those utilizing sequential batch reactor techniques or processes, require that clarified fluid be periodically withdrawn from the reactor or digester within which the process is occurring. Such decanters must be functional throughout the year, even in environments where the lower temperature extremes may form ice upon the upper layer of the fluid within the reactor. It is also important that the decanting system not entrain sludge during mix cycles within the reactor or have sludge settle within the decanting system such that when clarified liquid is withdrawn, a certain amount of sludge is withdrawn with the liquid, as such entrainment would discharge highly polluted effluent.
One of the major problems with previous decanter systems for use in batch reactors has been that a receiver for the decanter has had the interior thereof open to the fluid within the reactor during sludge mixing cycles. When the sludge is being mixed with the incoming effluent and the entire reactor is in a generally mixed state, sludge is near the top of the reactor as well as the bottom. If the receiver is open at this time, the sludge usually enters the receiver and settles therein during settling cycles.
Thereafter, when the clarified fluid is withdrawn through the receiver, the sludge that is within the receiver is entrained with the clarified fluid to pollute the effluent. One solution to this problem is to withdraw the clarified fluid with a pump and have a cycle at the beginning of the withdrawal of the clarified fluid in which a certain amount of this fluid is directed back to the reactor so as to return the entrained sludge. Such a solution requires a pump and control mechanism or the like and close control of the recycle of the clarified fluid to the reactor.
Other attempts to resolve the problem of the sludge settling within the receiver, have been directed to physically removing the receiver from the tank during mixing cycles. This typically requires a cumbersome and expensive structure which is suitably strong to hold a decanting system out of the reactor fluid during the mix cycle. In addition, where freezing is likely to occur, fluid within the decanting structure may freeze if raised from the liquid in the reactor or, the fluid level at the top of the reactor may freeze which may make it difficult or impossible to raise and lower the decanting structure and to raise or lower a decanter requires a mechanical mechanism that is affected by weather conditions and requires regular maintenance.
Other problems associated with the decanting structure are that the receiver should be sufficiently spaced from the sludge layer to prevent accidental intake of sludge into the receiver. In addition, the receiver should withdraw clarified fluid in such a manner that the withdrawn fluid does not entrain sludge due to high velocities of the withdrawn fluid coming from or near the sludge layer or because the withdrawn fluid is taken from directly above the sludge layer.
Also the support structure for the decanter system must allow for vertical movement of the receiver, as the upper liquid level in the reactor may vary substantially during the different cycles therein. Preferably, the support structure allows the receiver to be supported at a generally fixed height beneath the upper liquid level so as to prevent entrainment of floating debris or scum into the receiver and articulated sufficiently so that the receiver may move freely and smoothly vertically while the upper liquid level is varying.
Certain other devices are designed to draw clarified fluid from near the bottom of the reactor so that a siphon can control flow This draws from precisely the region of heavy sludge which should be avoided and should be drawn from the most clarified supernatant which is just below the liquid surface.
It is also noted that certain prior art decanting systems have incorporated extensive and expensive mechanical devices for manipulating the fluid receiver, sometimes into and out of the liquid layer within the reactor. The complex mechanical devices required for this operation are subject to failure and do not provide a simple and easy method of preventing sludge entry into the receiver. These devices often do not function well, if at all, where ice is floating on or forming upon the upper layer of the reactor and they require very level weirs so as to receive the liquid affluent evenly. These types of decanters in practice have proven to have problems maintaining a level weir, especially in the larger sizes.
Some of these problems have been addressed such as by U.S. Pat. No. 4,711,716 which discloses a floating decanter which includes flaps, nozzles, multiple ports, cover plate, etc. which teaches the float devices as intricate parts of the decanter and the decanter elements cannot be removed from a manway without removing the entire assembly including the floats.
The present invention addresses the above problems and teaches means to provide a simple floating decanter that is removable from above, i.e. the manway, leaving the floating device in the tank.